The present invention relates generally to a method and apparatus for embossing and crimping a multi-layer sheet material web assembly, and in particular, to a method and apparatus for embossing and crimping a multi-layer sheet material web by forming a pattern of embossments in the layers of the sheet material web assembly, a portion of which further comprise crimps to bind the layers together. The invention also relates to a multi-layer sheet material web assembly having a pattern of embossments and crimps.
It is well known in the field of paper making, and particularly in the field of manufacturing tissue products such as facial tissues, bath tissues and paper towels, to form a sheet material web assembly having a plurality of layers, or plies. Often, the individual layers of sheet material web, or the assembly as a whole, are provided with embossments, or raised portions, which can improve important product qualities of the assembly, such as the softness, water absorbency and bulk thereof. Often, the embossments are arranged in an aesthetically pleasing pattern to improve the overall appearance of the assembly.
In such multi-layer configurations, the individual layers of sheet material web are usually joined together to form the web assembly. Typically, the layers are joined with adhesives or crimping, or some combination thereof. Often, when crimping is used to bind the layers, the crimps are formed independent of the pattern of embossments, for example, in the form of lines running along the machine direction of the web assembly. Such crimp lines can interfere with the embossing pattern so as to detract from the pleasing appearance thereof. Alternatively, adhesives can be difficult to apply, and the application thereof can increase the cost of the web assembly.
Briefly stated, the invention is directed to an apparatus for embossing and crimping a plurality of layers of sheet material web to form a sheet material web assembly. The apparatus includes a first, second and third roll having substantially parallel axes of rotation. The first roll includes at least one element extending radially therefrom. The second roll has a resilient surface that engages the element of the first roll to form a first nip therebetween. The element is adapted to emboss concurrently the plurality of layers of sheet material web so as to form a plurality of embossments in each of the plurality of sheet material web layers as the layers are passed together through the first nip. The third roll has a non-resilient surface that engages the element of the first roll. The element of the first roll and the non-resilient surface of the third roll form a second nip therebetween. The element is adapted to crimp the plurality of layers of sheet material web together as they pass through the second nip.
In one embodiment, the first roll includes at least a first and second element extending radially therefrom, with the first element having a greater radial height than the second element. The first and second elements engage the resilient surface of the second roll to form a first nip therebetween. The non-resilient surface of the third roll is spaced apart from the second element of the first roll so as to avoid contact therewith, while the first element engages the non-resilient surface to form a second nip therebetween.
In a preferred embodiment, the first roll includes a plurality of first and second elements. Preferably, the first and second elements are arranged in a pattern so as to form a pattern of embossments on each of the layers of sheet material web as they pass through the first nip.
In another aspect of the invention, the apparatus further includes the plurality of layers of sheet material web, which are disposed in the first and second nips. Each layer of sheet material web includes a plurality of embossments formed by the first and second elements at the first nip. Each of the plurality of embossments in each layer of sheet material web is raised in the same direction and nests in the plurality of embossments raised in the other layers. The layers of sheet material web are joined by crimps formed by the first element at the second nip.
In another aspect of the invention, a method is provided for embossing and crimping the sheet material web assembly. The method includes the steps of passing the plurality of layers of sheet material web through the first nip, forming a plurality of embossments in each layer by pressing the layers between the element and the resilient surface of the second roll, passing the layers through the second nip and crimping the layers together by pressing the plurality of layers between the element and the non-resilient surface of the third roll.
In yet another aspect, a sheet material web assembly having a pattern of embossments and crimps is provided. The sheet material web assembly includes a plurality of layers of sheet material webs. Each layer of sheet material web includes a first and second surface, with the first surface of each layer facing the same direction as the first surfaces of the other layers. Each of the layers includes a plurality of embossments raised from the first surface and nesting within the plurality of embossments of the other layers. The embossments are arranged in a pattern on each layer, with a portion, or all, of the pattern of embossments further comprising a plurality of crimps binding the layers together.
The present invention provides significant advantages over other apparatuses and methods used to emboss and crimp multi-layer sheet material web assemblies. In particular, because the first elements of the first roll are used both to emboss and to crimp the plurality of layers, as the layers remain registered on the first elements as they pass through the first and second nips, the crimps can be incorporated into the pattern of embossments. In this way, the crimps, which attach or bind the plurality of layers of sheet material web together, can be hidden within the pattern of embossments, rather than interfering with the pattern, which can adversely affect the aesthetics of the sheet material web assembly.
In addition, instead of employing separate rolls to crimp and emboss the assembly, a single roll having elements that both crimp and emboss the sheet material web assembly can be used to emboss and crimp the layers of sheet material web. In this way, the assembly and maintenance costs of the apparatus and method can be reduced.
The present invention, together with further objects and advantages, will be best understood by reference to the following detailed description taken in conjunction with the accompanying drawings.